Manures and Manuring v, 
ficial manuring are understood, experiments should be 
made. 
There are a great many substances necessary as food 
for plants. The chief are: Carbon, oxygen, hydrogen, 
nitrogen, phosphorus, sulphur, potassium, calcium, mag- 
nesium, iron, sodium, manganese, silicon, and chlorine. 
Of these, nitrogen, phosphorus, and potassium are the 
three principal substances with which we have to deal in 
manuring our plants. 
Carbon is obtained from the carbon dioxide (C 0 2 ) of 
the atmosphere. Oxygen is obtained partly from the 
atmosphere and partly from water. Hydrogen and oxygen 
are taken up in the water, &c. The other substances are 
generally present in all soils in quantities large enough for 
the use of most plants. But plants never take up their 
food in the form of an element. It is always as a com- 
pound. Nitrogen is taken up in the form of nitrates, 
phosphorus in the form of phosphates, and potassium in 
the form of potash. 
For example: Nitrate of soda (NaNO s ) is sodium (Na), 
nitrogen (N), and oxygen ( 0 3 ); that is to say, i part of 
Na, i part of N, and 3 parts of O. Sulphate of potash 
(K 2 S 0 4 ) consists of potassium (K) 2 parts, sulphur (S) 
1 part, and oxygen (O) 4 parts; and superphosphates 
(Ca 3 P 2 O g ) consist of calcium (Ca) 3 parts, phosphorus (P) 
2 parts, and oxygen (O) 8 parts. Thus we see that the 
plant takes up many elements in combination. These 
are broken up within the plant for its individual use. 
We will now turn our attention to the three principal 
( classes of manures, and see how they benefit the crops. 
(C 525) 
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